在创建用于Mupdf的版本以读取加密的pdf文件时，我遇到了一些问题。我正在查看pdf_crypt.c文件，以了解如何完成此操作。但是我不知道该怎么做。
如果我用简单的话来说，
我正在发布pdf_crypt.c文件以供引用。
#include "mupdf/pdf.h"
enum
{
PDF_CRYPT_NONE,
PDF_CRYPT_RC4,
PDF_CRYPT_AESV2,
PDF_CRYPT_AESV3,
PDF_CRYPT_UNKNOWN,
};
enum
{
PDF_PERM_PRINT = 1 << 2,
PDF_PERM_CHANGE = 1 << 3,
PDF_PERM_COPY = 1 << 4,
PDF_PERM_NOTES = 1 << 5,
PDF_PERM_FILL_FORM = 1 << 8,
PDF_PERM_ACCESSIBILITY = 1 << 9,
PDF_PERM_ASSEMBLE = 1 << 10,
PDF_PERM_HIGH_RES_PRINT = 1 << 11,
PDF_DEFAULT_PERM_FLAGS = 0xfffc
};
typedef struct pdf_crypt_filter_s pdf_crypt_filter;
struct pdf_crypt_filter_s
{
int method;
int length;
};
struct pdf_crypt_s
{
pdf_obj *id;
int v;
int length;
pdf_obj *cf;
pdf_crypt_filter stmf;
pdf_crypt_filter strf;
int r;
unsigned char o[48];
unsigned char u[48];
unsigned char oe[32];
unsigned char ue[32];
int p;
int encrypt_metadata;
unsigned char key[32]; /* decryption key generated from password */
};
static void pdf_parse_crypt_filter(fz_context *ctx, pdf_crypt_filter *cf, pdf_crypt *crypt, pdf_obj *name);
/*
* Create crypt object for decrypting strings and streams
* given the Encryption and ID objects.
*/
pdf_crypt *
pdf_new_crypt(fz_context *ctx, pdf_obj *dict, pdf_obj *id)
{
pdf_crypt *crypt;
pdf_obj *obj;
crypt = fz_malloc_struct(ctx, pdf_crypt);
/* Common to all security handlers (PDF 1.7 table 3.18) */
obj = pdf_dict_get(ctx, dict, PDF_NAME_Filter);
if (!pdf_is_name(ctx, obj))
{
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "unspecified encryption handler");
}
if (!pdf_name_eq(ctx, PDF_NAME_Standard, obj) != 0)
{
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "unknown encryption handler: '%s'", pdf_to_name(ctx, obj));
}
crypt->v = 0;
obj = pdf_dict_get(ctx, dict, PDF_NAME_V);
if (pdf_is_int(ctx, obj))
crypt->v = pdf_to_int(ctx, obj);
if (crypt->v != 1 && crypt->v != 2 && crypt->v != 4 && crypt->v != 5)
{
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "unknown encryption version");
}
/* Standard security handler (PDF 1.7 table 3.19) */
obj = pdf_dict_get(ctx, dict, PDF_NAME_R);
if (pdf_is_int(ctx, obj))
crypt->r = pdf_to_int(ctx, obj);
else if (crypt->v <= 4)
{
fz_warn(ctx, "encryption dictionary missing revision value, guessing...");
if (crypt->v < 2)
crypt->r = 2;
else if (crypt->v == 2)
crypt->r = 3;
else if (crypt->v == 4)
crypt->r = 4;
}
else
{
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "encryption dictionary missing version and revision value");
}
if (crypt->r < 1 || crypt->r > 6)
{
int r = crypt->r;
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "unknown crypt revision %d", r);
}
obj = pdf_dict_get(ctx, dict, PDF_NAME_O);
if (pdf_is_string(ctx, obj) && pdf_to_str_len(ctx, obj) == 32)
memcpy(crypt->o, pdf_to_str_buf(ctx, obj), 32);
/* /O and /U are supposed to be 48 bytes long for revision 5 and 6, they're often longer, though */
else if (crypt->r >= 5 && pdf_is_string(ctx, obj) && pdf_to_str_len(ctx, obj) >= 48)
memcpy(crypt->o, pdf_to_str_buf(ctx, obj), 48);
else
{
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "encryption dictionary missing owner password");
}
obj = pdf_dict_get(ctx, dict, PDF_NAME_U);
if (pdf_is_string(ctx, obj) && pdf_to_str_len(ctx, obj) == 32)
memcpy(crypt->u, pdf_to_str_buf(ctx, obj), 32);
/* /O and /U are supposed to be 48 bytes long for revision 5 and 6, they're often longer, though */
else if (crypt->r >= 5 && pdf_is_string(ctx, obj) && pdf_to_str_len(ctx, obj) >= 48)
memcpy(crypt->u, pdf_to_str_buf(ctx, obj), 48);
else if (pdf_is_string(ctx, obj) && pdf_to_str_len(ctx, obj) < 32)
{
fz_warn(ctx, "encryption password key too short (%d)", pdf_to_str_len(ctx, obj));
memcpy(crypt->u, pdf_to_str_buf(ctx, obj), pdf_to_str_len(ctx, obj));
}
else
{
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "encryption dictionary missing user password");
}
obj = pdf_dict_get(ctx, dict, PDF_NAME_P);
if (pdf_is_int(ctx, obj))
crypt->p = pdf_to_int(ctx, obj);
else
{
fz_warn(ctx, "encryption dictionary missing permissions");
crypt->p = 0xfffffffc;
}
if (crypt->r == 5 || crypt->r == 6)
{
obj = pdf_dict_get(ctx, dict, PDF_NAME_OE);
if (!pdf_is_string(ctx, obj) || pdf_to_str_len(ctx, obj) != 32)
{
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "encryption dictionary missing owner encryption key");
}
memcpy(crypt->oe, pdf_to_str_buf(ctx, obj), 32);
obj = pdf_dict_get(ctx, dict, PDF_NAME_UE);
if (!pdf_is_string(ctx, obj) || pdf_to_str_len(ctx, obj) != 32)
{
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "encryption dictionary missing user encryption key");
}
memcpy(crypt->ue, pdf_to_str_buf(ctx, obj), 32);
}
crypt->encrypt_metadata = 1;
obj = pdf_dict_get(ctx, dict, PDF_NAME_EncryptMetadata);
if (pdf_is_bool(ctx, obj))
crypt->encrypt_metadata = pdf_to_bool(ctx, obj);
/* Extract file identifier string */
if (pdf_is_array(ctx, id) && pdf_array_len(ctx, id) == 2)
{
obj = pdf_array_get(ctx, id, 0);
if (pdf_is_string(ctx, obj))
crypt->id = pdf_keep_obj(ctx, obj);
}
else
fz_warn(ctx, "missing file identifier, may not be able to do decryption");
/* Determine encryption key length */
crypt->length = 40;
if (crypt->v == 2 || crypt->v == 4)
{
obj = pdf_dict_get(ctx, dict, PDF_NAME_Length);
if (pdf_is_int(ctx, obj))
crypt->length = pdf_to_int(ctx, obj);
/* work-around for pdf generators that assume length is in bytes */
if (crypt->length < 40)
crypt->length = crypt->length * 8;
if (crypt->length % 8 != 0)
{
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "invalid encryption key length");
}
if (crypt->length < 40 || crypt->length > 128)
{
pdf_drop_crypt(ctx, crypt);
fz_throw(ctx, FZ_ERROR_GENERIC, "invalid encryption key length");
}
}
if (crypt->v == 5)
crypt->length = 256;
if (crypt->v == 1 || crypt->v == 2)
{
crypt->stmf.method = PDF_CRYPT_RC4;
crypt->stmf.length = crypt->length;
crypt->strf.method = PDF_CRYPT_RC4;
crypt->strf.length = crypt->length;
}
if (crypt->v == 4 || crypt->v == 5)
{
crypt->stmf.method = PDF_CRYPT_NONE;
crypt->stmf.length = crypt->length;
crypt->strf.method = PDF_CRYPT_NONE;
crypt->strf.length = crypt->length;
obj = pdf_dict_get(ctx, dict, PDF_NAME_CF);
if (pdf_is_dict(ctx, obj))
{
crypt->cf = pdf_keep_obj(ctx, obj);
}
else
{
crypt->cf = NULL;
}
fz_try(ctx)
{
obj = pdf_dict_get(ctx, dict, PDF_NAME_StmF);
if (pdf_is_name(ctx, obj))
pdf_parse_crypt_filter(ctx, &crypt->stmf, crypt, obj);
obj = pdf_dict_get(ctx, dict, PDF_NAME_StrF);
if (pdf_is_name(ctx, obj))
pdf_parse_crypt_filter(ctx, &crypt->strf, crypt, obj);
}
fz_catch(ctx)
{
pdf_drop_crypt(ctx, crypt);
fz_rethrow_message(ctx, "cannot parse string crypt filter (%d %d R)", pdf_to_num(ctx, obj), pdf_to_gen(ctx, obj));
}
/* in crypt revision 4, the crypt filter determines the key length */
if (crypt->strf.method != PDF_CRYPT_NONE)
crypt->length = crypt->stmf.length;
}
return crypt;
}
void
pdf_drop_crypt(fz_context *ctx, pdf_crypt *crypt)
{
pdf_drop_obj(ctx, crypt->id);
pdf_drop_obj(ctx, crypt->cf);
fz_free(ctx, crypt);
}
/*
* Parse a CF dictionary entry (PDF 1.7 table 3.22)
*/
static void
pdf_parse_crypt_filter(fz_context *ctx, pdf_crypt_filter *cf, pdf_crypt *crypt, pdf_obj *name)
{
pdf_obj *obj;
pdf_obj *dict;
int is_identity = (pdf_name_eq(ctx, name, PDF_NAME_Identity));
int is_stdcf = (!is_identity && pdf_name_eq(ctx, name, PDF_NAME_StdCF));
if (!is_identity && !is_stdcf)
fz_throw(ctx, FZ_ERROR_GENERIC, "Crypt Filter not Identity or StdCF (%d %d R)", pdf_to_num(ctx, crypt->cf), pdf_to_gen(ctx, crypt->cf));
cf->method = PDF_CRYPT_NONE;
cf->length = crypt->length;
if (!crypt->cf)
{
cf->method = (is_identity ? PDF_CRYPT_NONE : PDF_CRYPT_RC4);
return;
}
dict = pdf_dict_get(ctx, crypt->cf, name);
if (!pdf_is_dict(ctx, dict))
fz_throw(ctx, FZ_ERROR_GENERIC, "cannot parse crypt filter (%d %d R)", pdf_to_num(ctx, crypt->cf), pdf_to_gen(ctx, crypt->cf));
obj = pdf_dict_get(ctx, dict, PDF_NAME_CFM);
if (pdf_is_name(ctx, obj))
{
if (pdf_name_eq(ctx, PDF_NAME_None, obj))
cf->method = PDF_CRYPT_NONE;
else if (pdf_name_eq(ctx, PDF_NAME_V2, obj))
cf->method = PDF_CRYPT_RC4;
else if (pdf_name_eq(ctx, PDF_NAME_AESV2, obj))
cf->method = PDF_CRYPT_AESV2;
else if (pdf_name_eq(ctx, PDF_NAME_AESV3, obj))
cf->method = PDF_CRYPT_AESV3;
else
fz_warn(ctx, "unknown encryption method: %s", pdf_to_name(ctx, obj));
}
obj = pdf_dict_get(ctx, dict, PDF_NAME_Length);
if (pdf_is_int(ctx, obj))
cf->length = pdf_to_int(ctx, obj);
/* the length for crypt filters is supposed to be in bytes not bits */
if (cf->length < 40)
cf->length = cf->length * 8;
if ((cf->length % 8) != 0)
fz_throw(ctx, FZ_ERROR_GENERIC, "invalid key length: %d", cf->length);
if ((crypt->r == 1 || crypt->r == 2 || crypt->r == 3 || crypt->r == 4) &&
(cf->length < 0 || cf->length > 128))
fz_throw(ctx, FZ_ERROR_GENERIC, "invalid key length: %d", cf->length);
if ((crypt->r == 5 || crypt->r == 6) && cf->length != 256)
fz_throw(ctx, FZ_ERROR_GENERIC, "invalid key length: %d", cf->length);
}
/*
* Compute an encryption key (PDF 1.7 algorithm 3.2)
*/
static const unsigned char padding[32] =
{
0x28, 0xbf, 0x4e, 0x5e, 0x4e, 0x75, 0x8a, 0x41,
0x64, 0x00, 0x4e, 0x56, 0xff, 0xfa, 0x01, 0x08,
0x2e, 0x2e, 0x00, 0xb6, 0xd0, 0x68, 0x3e, 0x80,
0x2f, 0x0c, 0xa9, 0xfe, 0x64, 0x53, 0x69, 0x7a
};
static void
pdf_compute_encryption_key(fz_context *ctx, pdf_crypt *crypt, unsigned char *password, int pwlen, unsigned char *key)
{
unsigned char buf[32];
unsigned int p;
int i, n;
fz_md5 md5;
n = crypt->length / 8;
/* Step 1 - copy and pad password string */
if (pwlen > 32)
pwlen = 32;
memcpy(buf, password, pwlen);
memcpy(buf + pwlen, padding, 32 - pwlen);
/* Step 2 - init md5 and pass value of step 1 */
fz_md5_init(&md5);
fz_md5_update(&md5, buf, 32);
/* Step 3 - pass O value */
fz_md5_update(&md5, crypt->o, 32);
/* Step 4 - pass P value as unsigned int, low-order byte first */
p = (unsigned int) crypt->p;
buf[0] = (p) & 0xFF;
buf[1] = (p >> 8) & 0xFF;
buf[2] = (p >> 16) & 0xFF;
buf[3] = (p >> 24) & 0xFF;
fz_md5_update(&md5, buf, 4);
/* Step 5 - pass first element of ID array */
fz_md5_update(&md5, (unsigned char *)pdf_to_str_buf(ctx, crypt->id), pdf_to_str_len(ctx, crypt->id));
/* Step 6 (revision 4 or greater) - if metadata is not encrypted pass 0xFFFFFFFF */
if (crypt->r >= 4)
{
if (!crypt->encrypt_metadata)
{
buf[0] = 0xFF;
buf[1] = 0xFF;
buf[2] = 0xFF;
buf[3] = 0xFF;
fz_md5_update(&md5, buf, 4);
}
}
/* Step 7 - finish the hash */
fz_md5_final(&md5, buf);
/* Step 8 (revision 3 or greater) - do some voodoo 50 times */
if (crypt->r >= 3)
{
for (i = 0; i < 50; i++)
{
fz_md5_init(&md5);
fz_md5_update(&md5, buf, n);
fz_md5_final(&md5, buf);
}
}
/* Step 9 - the key is the first 'n' bytes of the result */
memcpy(key, buf, n);
}
/*
* Compute an encryption key (PDF 1.7 ExtensionLevel 3 algorithm 3.2a)
*/
static void
pdf_compute_encryption_key_r5(fz_context *ctx, pdf_crypt *crypt, unsigned char *password, int pwlen, int ownerkey, unsigned char *validationkey)
{
unsigned char buffer[128 + 8 + 48];
fz_sha256 sha256;
fz_aes aes;
/* Step 2 - truncate UTF-8 password to 127 characters */
if (pwlen > 127)
pwlen = 127;
/* Step 3/4 - test password against owner/user key and compute encryption key */
memcpy(buffer, password, pwlen);
if (ownerkey)
{
memcpy(buffer + pwlen, crypt->o + 32, 8);
memcpy(buffer + pwlen + 8, crypt->u, 48);
}
else
memcpy(buffer + pwlen, crypt->u + 32, 8);
fz_sha256_init(&sha256);
fz_sha256_update(&sha256, buffer, pwlen + 8 + (ownerkey ? 48 : 0));
fz_sha256_final(&sha256, validationkey);
/* Step 3.5/4.5 - compute file encryption key from OE/UE */
memcpy(buffer + pwlen, crypt->u + 40, 8);
fz_sha256_init(&sha256);
fz_sha256_update(&sha256, buffer, pwlen + 8);
fz_sha256_final(&sha256, buffer);
/* clear password buffer and use it as iv */
memset(buffer + 32, 0, sizeof(buffer) - 32);
if (aes_setkey_dec(&aes, buffer, crypt->length))
fz_throw(ctx, FZ_ERROR_GENERIC, "AES key init failed (keylen=%d)", crypt->length);
aes_crypt_cbc(&aes, AES_DECRYPT, 32, buffer + 32, ownerkey ? crypt->oe : crypt->ue, crypt->key);
}
/*
* Compute an encryption key (PDF 1.7 ExtensionLevel 8 algorithm)
*
* Adobe has not yet released the details, so the algorithm reference is:
* http://esec-lab.sogeti.com/post/The-undocumented-password-validation-algorithm-of-Adobe-Reader-X
*/
static void
pdf_compute_hardened_hash_r6(fz_context *ctx, unsigned char *password, int pwlen, unsigned char salt[16], unsigned char *ownerkey, unsigned char hash[32])
{
unsigned char data[(128 + 64 + 48) * 64];
unsigned char block[64];
int block_size = 32;
int data_len = 0;
int i, j, sum;
fz_sha256 sha256;
fz_sha384 sha384;
fz_sha512 sha512;
fz_aes aes;
/* Step 1: calculate initial data block */
fz_sha256_init(&sha256);
fz_sha256_update(&sha256, password, pwlen);
fz_sha256_update(&sha256, salt, 8);
if (ownerkey)
fz_sha256_update(&sha256, ownerkey, 48);
fz_sha256_final(&sha256, block);
for (i = 0; i < 64 || i < data[data_len * 64 - 1] + 32; i++)
{
/* Step 2: repeat password and data block 64 times */
memcpy(data, password, pwlen);
memcpy(data + pwlen, block, block_size);
if (ownerkey)
memcpy(data + pwlen + block_size, ownerkey, 48);
data_len = pwlen + block_size + (ownerkey ? 48 : 0);
for (j = 1; j < 64; j++)
memcpy(data + j * data_len, data, data_len);
/* Step 3: encrypt data using data block as key and iv */
if (aes_setkey_enc(&aes, block, 128))
fz_throw(ctx, FZ_ERROR_GENERIC, "AES key init failed (keylen=%d)", 128);
aes_crypt_cbc(&aes, AES_ENCRYPT, data_len * 64, block + 16, data, data);
/* Step 4: determine SHA-2 hash size for this round */
for (j = 0, sum = 0; j < 16; j++)
sum += data[j];
/* Step 5: calculate data block for next round */
block_size = 32 + (sum % 3) * 16;
switch (block_size)
{
case 32:
fz_sha256_init(&sha256);
fz_sha256_update(&sha256, data, data_len * 64);
fz_sha256_final(&sha256, block);
break;
case 48:
fz_sha384_init(&sha384);
fz_sha384_update(&sha384, data, data_len * 64);
fz_sha384_final(&sha384, block);
break;
case 64:
fz_sha512_init(&sha512);
fz_sha512_update(&sha512, data, data_len * 64);
fz_sha512_final(&sha512, block);
break;
}
}
memset(data, 0, sizeof(data));
memcpy(hash, block, 32);
}
static void
pdf_compute_encryption_key_r6(fz_context *ctx, pdf_crypt *crypt, unsigned char *password, int pwlen, int ownerkey, unsigned char *validationkey)
{
unsigned char hash[32];
unsigned char iv[16];
fz_aes aes;
if (pwlen > 127)
pwlen = 127;
pdf_compute_hardened_hash_r6(ctx, password, pwlen,
(ownerkey ? crypt->o : crypt->u) + 32,
ownerkey ? crypt->u : NULL, validationkey);
pdf_compute_hardened_hash_r6(ctx, password, pwlen,
crypt->u + 40, NULL, hash);
memset(iv, 0, sizeof(iv));
if (aes_setkey_dec(&aes, hash, 256))
fz_throw(ctx, FZ_ERROR_GENERIC, "AES key init failed (keylen=256)");
aes_crypt_cbc(&aes, AES_DECRYPT, 32, iv,
ownerkey ? crypt->oe : crypt->ue, crypt->key);
}
/*
* Computing the user password (PDF 1.7 algorithm 3.4 and 3.5)
* Also save the generated key for decrypting objects and streams in crypt->key.
*/
static void
pdf_compute_user_password(fz_context *ctx, pdf_crypt *crypt, unsigned char *password, int pwlen, unsigned char *output)
{
if (crypt->r == 2)
{
fz_arc4 arc4;
pdf_compute_encryption_key(ctx, crypt, password, pwlen, crypt->key);
fz_arc4_init(&arc4, crypt->key, crypt->length / 8);
fz_arc4_encrypt(&arc4, output, padding, 32);
}
if (crypt->r == 3 || crypt->r == 4)
{
unsigned char xor[32];
unsigned char digest[16];
fz_md5 md5;
fz_arc4 arc4;
int i, x, n;
n = crypt->length / 8;
pdf_compute_encryption_key(ctx, crypt, password, pwlen, crypt->key);
fz_md5_init(&md5);
fz_md5_update(&md5, padding, 32);
fz_md5_update(&md5, (unsigned char*)pdf_to_str_buf(ctx, crypt->id), pdf_to_str_len(ctx, crypt->id));
fz_md5_final(&md5, digest);
fz_arc4_init(&arc4, crypt->key, n);
fz_arc4_encrypt(&arc4, output, digest, 16);
for (x = 1; x <= 19; x++)
{
for (i = 0; i < n; i++)
xor[i] = crypt->key[i] ^ x;
fz_arc4_init(&arc4, xor, n);
fz_arc4_encrypt(&arc4, output, output, 16);
}
memcpy(output + 16, padding, 16);
}
if (crypt->r == 5)
{
pdf_compute_encryption_key_r5(ctx, crypt, password, pwlen, 0, output);
}
if (crypt->r == 6)
{
pdf_compute_encryption_key_r6(ctx, crypt, password, pwlen, 0, output);
}
}
/*
* Authenticating the user password (PDF 1.7 algorithm 3.6
* and ExtensionLevel 3 algorithm 3.11)
* This also has the side effect of saving a key generated
* from the password for decrypting objects and streams.
*/
static int
pdf_authenticate_user_password(fz_context *ctx, pdf_crypt *crypt, unsigned char *password, int pwlen)
{
unsigned char output[32];
pdf_compute_user_password(ctx, crypt, password, pwlen, output);
if (crypt->r == 2 || crypt->r == 5 || crypt->r == 6)
return memcmp(output, crypt->u, 32) == 0;
if (crypt->r == 3 || crypt->r == 4)
return memcmp(output, crypt->u, 16) == 0;
return 0;
}
/*
* Authenticating the owner password (PDF 1.7 algorithm 3.7
* and ExtensionLevel 3 algorithm 3.12)
* Generates the user password from the owner password
* and calls pdf_authenticate_user_password.
*/
static int
pdf_authenticate_owner_password(fz_context *ctx, pdf_crypt *crypt, unsigned char *ownerpass, int pwlen)
{
unsigned char pwbuf[32];
unsigned char key[32];
unsigned char xor[32];
unsigned char userpass[32];
int i, n, x;
fz_md5 md5;
fz_arc4 arc4;
if (crypt->r == 5)
{
/* PDF 1.7 ExtensionLevel 3 algorithm 3.12 */
pdf_compute_encryption_key_r5(ctx, crypt, ownerpass, pwlen, 1, key);
return !memcmp(key, crypt->o, 32);
}
else if (crypt->r == 6)
{
/* PDF 1.7 ExtensionLevel 8 algorithm */
pdf_compute_encryption_key_r6(ctx, crypt, ownerpass, pwlen, 1, key);
return !memcmp(key, crypt->o, 32);
}
n = crypt->length / 8;
/* Step 1 -- steps 1 to 4 of PDF 1.7 algorithm 3.3 */
/* copy and pad password string */
if (pwlen > 32)
pwlen = 32;
memcpy(pwbuf, ownerpass, pwlen);
memcpy(pwbuf + pwlen, padding, 32 - pwlen);
/* take md5 hash of padded password */
fz_md5_init(&md5);
fz_md5_update(&md5, pwbuf, 32);
fz_md5_final(&md5, key);
/* do some voodoo 50 times (Revision 3 or greater) */
if (crypt->r >= 3)
{
for (i = 0; i < 50; i++)
{
fz_md5_init(&md5);
fz_md5_update(&md5, key, 16);
fz_md5_final(&md5, key);
}
}
/* Step 2 (Revision 2) */
if (crypt->r == 2)
{
fz_arc4_init(&arc4, key, n);
fz_arc4_encrypt(&arc4, userpass, crypt->o, 32);
}
/* Step 2 (Revision 3 or greater) */
if (crypt->r >= 3)
{
memcpy(userpass, crypt->o, 32);
for (x = 0; x < 20; x++)
{
for (i = 0; i < n; i++)
xor[i] = key[i] ^ (19 - x);
fz_arc4_init(&arc4, xor, n);
fz_arc4_encrypt(&arc4, userpass, userpass, 32);
}
}
return pdf_authenticate_user_password(ctx, crypt, userpass, 32);
}
static void pdf_docenc_from_utf8(char *password, const char *utf8, int n)
{
int i = 0, k, c;
while (*utf8 && i + 1 < n)
{
utf8 += fz_chartorune(&c, utf8);
for (k = 0; k < 256; k++)
{
if (c == pdf_doc_encoding[k])
{
password[i++] = k;
break;
}
}
/* FIXME: drop characters that can't be encoded or return an error? */
}
password[i] = 0;
}
static void pdf_saslprep_from_utf8(char *password, const char *utf8, int n)
{
/* TODO: stringprep with SALSprep profile */
fz_strlcpy(password, utf8, n);
}
int
pdf_authenticate_password(fz_context *ctx, pdf_document *doc, const char *pwd_utf8)
{
char password[2048];
if (doc->crypt)
{
password[0] = 0;
if (pwd_utf8)
{
if (doc->crypt->r <= 4)
pdf_docenc_from_utf8(password, pwd_utf8, sizeof password);
else
pdf_saslprep_from_utf8(password, pwd_utf8, sizeof password);
}
if (pdf_authenticate_user_password(ctx, doc->crypt, (unsigned char *)password, strlen(password)))
return 1;
if (pdf_authenticate_owner_password(ctx, doc->crypt, (unsigned char *)password, strlen(password)))
return 1;
return 0;
}
return 1;
}
int
pdf_needs_password(fz_context *ctx, pdf_document *doc)
{
if (!doc->crypt)
return 0;
if (pdf_authenticate_password(ctx, doc, ""))
return 0;
return 1;
}
int
pdf_has_permission(fz_context *ctx, pdf_document *doc, fz_permission p)
{
if (!doc->crypt)
return 1;
switch (p)
{
case FZ_PERMISSION_PRINT: return doc->crypt->p & PDF_PERM_PRINT;
case FZ_PERMISSION_COPY: return doc->crypt->p & PDF_PERM_COPY;
case FZ_PERMISSION_EDIT: return doc->crypt->p & PDF_PERM_CHANGE;
case FZ_PERMISSION_ANNOTATE: return doc->crypt->p & PDF_PERM_NOTES;
}
return 1;
}
unsigned char *
pdf_crypt_key(fz_context *ctx, pdf_document *doc)
{
if (doc->crypt)
return doc->crypt->key;
return NULL;
}
int
pdf_crypt_version(fz_context *ctx, pdf_document *doc)
{
if (doc->crypt)
return doc->crypt->v;
return 0;
}
int pdf_crypt_revision(fz_context *ctx, pdf_document *doc)
{
if (doc->crypt)
return doc->crypt->r;
return 0;
}
char *
pdf_crypt_method(fz_context *ctx, pdf_document *doc)
{
if (doc->crypt)
{
switch (doc->crypt->strf.method)
{
case PDF_CRYPT_NONE: return "None";
case PDF_CRYPT_RC4: return "RC4";
case PDF_CRYPT_AESV2: return "AES";
case PDF_CRYPT_AESV3: return "AES";
case PDF_CRYPT_UNKNOWN: return "Unknown";
}
}
return "None";
}
int
pdf_crypt_length(fz_context *ctx, pdf_document *doc)
{
if (doc->crypt)
return doc->crypt->length;
return 0;
}
/*
* PDF 1.7 algorithm 3.1 and ExtensionLevel 3 algorithm 3.1a
*
* Using the global encryption key that was generated from the
* password, create a new key that is used to decrypt individual
* objects and streams. This key is based on the object and
* generation numbers.
*/
static int
pdf_compute_object_key(pdf_crypt *crypt, pdf_crypt_filter *cf, int num, int gen, unsigned char *key, int max_len)
{
fz_md5 md5;
unsigned char message[5];
int key_len = crypt->length / 8;
if (key_len > max_len)
key_len = max_len;
if (cf->method == PDF_CRYPT_AESV3)
{
memcpy(key, crypt->key, key_len);
return key_len;
}
fz_md5_init(&md5);
fz_md5_update(&md5, crypt->key, key_len);
message[0] = (num) & 0xFF;
message[1] = (num >> 8) & 0xFF;
message[2] = (num >> 16) & 0xFF;
message[3] = (gen) & 0xFF;
message[4] = (gen >> 8) & 0xFF;
fz_md5_update(&md5, message, 5);
if (cf->method == PDF_CRYPT_AESV2)
fz_md5_update(&md5, (unsigned char *)"sAlT", 4);
fz_md5_final(&md5, key);
if (key_len + 5 > 16)
return 16;
return key_len + 5;
}
/*
* PDF 1.7 algorithm 3.1 and ExtensionLevel 3 algorithm 3.1a
*
* Decrypt all strings in obj modifying the data in-place.
* Recurse through arrays and dictionaries, but do not follow
* indirect references.
*/
static void
pdf_crypt_obj_imp(fz_context *ctx, pdf_crypt *crypt, pdf_obj *obj, unsigned char *key, int keylen)
{
unsigned char *s;
int i, n;
if (pdf_is_indirect(ctx, obj))
return;
if (pdf_is_string(ctx, obj))
{
s = (unsigned char *)pdf_to_str_buf(ctx, obj);
n = pdf_to_str_len(ctx, obj);
if (crypt->strf.method == PDF_CRYPT_RC4)
{
fz_arc4 arc4;
fz_arc4_init(&arc4, key, keylen);
fz_arc4_encrypt(&arc4, s, s, n);
}
if (crypt->strf.method == PDF_CRYPT_AESV2 || crypt->strf.method == PDF_CRYPT_AESV3)
{
if (n == 0)
{
/* Empty strings are permissible */
}
else if (n & 15 || n < 32)
fz_warn(ctx, "invalid string length for aes encryption");
else
{
unsigned char iv[16];
fz_aes aes;
memcpy(iv, s, 16);
if (aes_setkey_dec(&aes, key, keylen * 8))
fz_throw(ctx, FZ_ERROR_GENERIC, "AES key init failed (keylen=%d)", keylen * 8);
aes_crypt_cbc(&aes, AES_DECRYPT, n - 16, iv, s + 16, s);
/* delete space used for iv and padding bytes at end */
if (s[n - 17] < 1 || s[n - 17] > 16)
fz_warn(ctx, "aes padding out of range");
else
pdf_set_str_len(ctx, obj, n - 16 - s[n - 17]);
}
}
}
else if (pdf_is_array(ctx, obj))
{
n = pdf_array_len(ctx, obj);
for (i = 0; i < n; i++)
{
pdf_crypt_obj_imp(ctx, crypt, pdf_array_get(ctx, obj, i), key, keylen);
}
}
else if (pdf_is_dict(ctx, obj))
{
n = pdf_dict_len(ctx, obj);
for (i = 0; i < n; i++)
{
pdf_crypt_obj_imp(ctx, crypt, pdf_dict_get_val(ctx, obj, i), key, keylen);
}
}
}
void
pdf_crypt_obj(fz_context *ctx, pdf_crypt *crypt, pdf_obj *obj, int num, int gen)
{
unsigned char key[32];
int len;
len = pdf_compute_object_key(crypt, &crypt->strf, num, gen, key, 32);
pdf_crypt_obj_imp(ctx, crypt, obj, key, len);
}
最佳答案
首先，我要谈谈许可。 MuPDF已获得2种不同的许可。
第一个是GNU AGPL。这是一个非常严格的许可证，对您提出了很多要求，以便您可以使用代码。最大的要求是，获得应用程序副本的任何人都有权要求整个应用程序的完整源代码。这显然包括任何解密密钥，这意味着您的DRM将无用。在继续操作之前，您应该仔细阅读许可以确保它适合您想要的操作。
如果您在GNU AGPL许可下使用MuPDF，我们不能保证您会获得任何支持。
如果您不能遵守GNU AGPL的条款，则可以从Artifex获得商业许可(发送电子邮件至[email protected]，其中包含您项目的尽可能多的详细信息，他们将与您讨论定制许可的问题。提案)。这使您摆脱了GNU AGPL的所有繁重条款。
如果您不能遵守GNU AGPL，或者您不愿意支付商业许可，则不能使用MuPDF。
现在，进入实际问题...
pdf_crypt.c实现了PDF中使用的标准解密处理程序。在我看来，您想做一些非标准的事情。因此，pdf_crypt.c将需要进行一些更改。
一种技术是使用密码来创建完全正常的加密PDF文件。您的应用程序可以在打开文件时将密码提供给MuPDF，解密将对您无缝地进行。用户甚至不需要知道所涉及的密码。就编码而言，这是最简单的方法。
另一种技术是对文件进行基于块的加密，并在加载文件时解密文件的块-我们有这样的客户在其产品中进行DRM处理。
在不了解您想做什么的情况下无法为您提供更多信息。
如果您想进一步讨论这个问题，最好的选择是访问#ghostscript irc channel (有关在Web浏览器中打开此链接的链接，请参见mupdf.com)。
关于c++ - Mupdf加密解密问题，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/29669522/